1. Field of the Invention
The invention relates to an exhaust gas turbocharger for an internal combustion engine and specifically to the turbine portion having variably adjustable blades.
2. Description of Related Art
A generic exhaust gas turbine for a turbocharger is disclosed in DE 195 43 190 C2 which shows adjustable stop bodies in an annular nozzle arrangement to provide a variable adjustable blade arrangement. The stop bodies are utilized to increase the operating reliability of the exhaust gas turbine particularly in an engine braking mode of operation.
In addition, DE 198 38 928 C1 discloses in an exhaust gas turbocharger a turbine portion having a variably adjustable series of guide-blades. For each guide-blade, a sealing element is provided and located in a pressurized space. The sealing element design is in the form of sealing cups adapted to be sealingly pressed onto the free end of a blade so that the series gap formed at the end of the blade is completely sealed off. A disadvantage of this, however, is that a large number of sealing elements is required, one for each blade, and this increases expense and the susceptibility to operating faults. Furthermore, during adjustment of the blade and sealing member high adjusting forces have to be exerted to overcome frictional forces generated by pressing the sealing element onto the blade. Moreover, there is the risk of damage caused by a complete elimination of the end gap which allows an undesirably high rotational speed of the turbocharger particularly in an engine braking mode from relatively high engine speeds. Another problem with this seal design may occur by an undesirably great thermal expansion of an associated blade.
Another device is shown in JP 001 130002 AA which discloses an adjustable series of blades in which a precisely defined sealing gap is set by means of a spacer member.